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Journal of Hazardous Materials 143 (2007) 662–667

Ferritization treatment of copper in soil by electrokinetic remediation

Tomoyuki Kimura, Ken-Ichi Takase, Norifumi Terui, Shunitz Tanaka ∗Division of Material Science, Faculty of Environmental Earth Science, Hokkaido University, N10 W5, Kita-Ku, Sapporo 060-0810, Japan

Available online 9 January 2007

bstract

The usefulness of the combined use of the electrokinetic (EK) remediation and a ferrite treatment zone (FTZ) was demonstrated for a treatmentf the contaminated soil with heavy metal ions. Copper ions in contaminated soil were transferred into the FTZ by the EK technology and wereerritized in this system. The distribution of copper in a migration chamber after EK treatment with FTZ for 48 h showed the large difference in the

otal and eluted concentration of copper. This indicated that copper ions transferred by EK into the FTZ were ferritized there with ferrite reagent inoil alkalified by EK process. The copper–ferrite compound, which was not dissolved with diluted acid, was retained in the FTZ and accumulatedhere. The ratio of the ferritized amount of copper against total copper was 92% in the EK process with FTZ after 48 h.

2007 Elsevier B.V. All rights reserved.

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eywords: Electrokinetic remediation; Copper; Ferrite; Insolubilization; Soil

. Introduction

In our environment, there are many land sites contaminatedith a variety of pollutants. If the contaminated soils are leftithout any adequate treatment, it leads to the subsequent con-

aminations of ecosystem and foods through river and groundater as well as lands. Therefore, the development of the tech-ologies for cleaning up the contaminated soil is importantrom the viewpoint of the environmental protection. A varietyf treatment techniques for the soil contaminated with metalsr organic pollutants have been designed, using bioremediation1–5], phytoremediation [6–10], physical and chemical remedi-tion [11–13] and so on. These treatment methods for hazardousaterials in soil can be categorized into the in situ and ex

itu technology. The in situ technology, which treatment is per-ormed at the position of the contaminated site, is more efficientn the total-cost and applied time than the ex situ technology,ven though most of the current treatment methods applied tohe actual contaminated sites are ex situ technology.

Electrokinetic (EK) remediation is one of the in situ tech-ologies for removing pollutants from clayey soils on the basis

f electrokinetic phenomena [14]. The EK process is suitableor treating various contaminants (e.g. heavy metals, organicollutants and radionuclides) in many kinds of soils [15,16].

∗ Corresponding author. Tel.: +81 11 706 2219; fax: +81 11 706 2219.E-mail address: shunitz@ees.hokudai.ac.jp (S. Tanaka).

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304-3894/$ – see front matter © 2007 Elsevier B.V. All rights reserved.oi:10.1016/j.jhazmat.2007.01.010

his method can be performed under a low-level voltage or cur-ent between the electrodes, which are inserted in the vicinityf the contaminated sites. The charged species can be removedy electromigration and also the electrically neutral species bylectro-osmotic flow (EOF) in EK method if they are soluble inater.Although the EK technology is effective to remove heavy

etals in contaminated soil, the complete removal of heavy met-ls from soil by EK technology is sometimes difficult, becauselkalization of soil by applying voltage caused the precipitationf heavy metal ions in soil. The redox condition of soil alsonfluences the mobility of heavy metal ions and then the mobil-ties of metal ions in the presence of reducing and oxidizingeagents were investigated [17,18]. While, if heavy metal ionsan be accumulated at the limited area of soil, it may become anlternative technology.

The reactive zone where the granular iron (Fe0) was mixedith soil for entrapping or decomposing contaminants inroundwater has gained widespread acceptance in the environ-ental remediation and regulatory communities in recent years

19]. This reactive zone is called as a permeable reactive bar-ier (PRBs). Considerable investigation has been made towardnderstanding the interfacial chemistry of granular iron and theechanisms of the degradation of contaminants. However, less

ttention has been paid to the means for introduction of groundater and waste water into PRBs. Ho et al. reported that TCE in

he soil was removed and degraded by the combination of EKechnology with PRBs (it is called as Lasagna technology) [20].

T. Kimura et al. / Journal of Hazardous Materials 143 (2007) 662–667 663

Table 1The chemical property of the kaolin soil before and after the acid washing

Original kaolin Treated kaolin

pH 3.62 6.54Total organic carbon (TOC) N.D. (ppm) N.D. (ppm)

Ratio of mineralSiO2 79.72 79.55Al2O3 17.57 18.90TiO2 0.76 0.37K2O 0.68 0.42Cl 0.29 0.11Fe O 0.27 0.15

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Table 2The element of poly ferric sulfate solution

Specific gravity (20 ◦C) 1.506Fe3+ 11.1%Fe2+ 0.01%Pb 2 ppmCd N.D. (ppm)Total-Hg N.D. (ppm)Ap

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7pTply as a function of time. The effluent by EOF was collected ina measuring cylinder and stored for analysis. The constant dcvoltage of 20 V (the potential gradient is 2.0 V/cm) was appliedthrough the soil for 0–96 h.

2 3

SO2 0.17 0.13SrO 0.07 0.04

e also reported the removal and the degradation of TCE in theoil by the combination of EK technology with PRBs [21].

The ferrite method not only insolubilizes metal ions but alsohanges metal ions to the magnetic material. The ferritizations able to remove many kinds of harmful metal ions at theame time, and can be applied to the treatment of Cr6+ and

n7+ without especial pre-treatment [22]. Ferritized metals cane separated easily by sedimentation or magnetic separation23].

The purpose of this study is to confirm the usefulness of theombined use of the EK remediation and a ferrite treatmentone (FTZ). This system includes two treatment processes. Ones an EK system, where heavy metal ions are removed from aontaminated soil by electromigration and electroosmotic flow,nd the metal ions are introduced into the FTZ by EK.

The second is a FTZ system, where metal ions are ferritized toe immobilized as ferrite material. The immobilization of heavyetal ions by ferritization is effective for the treatment of the site

ontaminated with heavy metals of relative low concentration. Inhis case, a large amount of water produced by EK process shoulde treated. In the combined system of EK with FTZ, if metalons are accumulated completely in FTZ, it is not necessary toreat water produced by EK. Generally, both of acidification andlkalization of soil caused by electrolysis of water at the EKystem without a buffer supplying system and an ion exchangeembrane filter [16]. However, the ferritization of metal ionsas performed under alkali condition effectively. Alkalizationf soil by EK process is suitable to the condition for ferritization.

. Materials and methods

.1. Soil and materials

Commercial available kaolin, which mainly consists of kaoli-ite, from Wako Pure Chemical Co. (Tokyo, Japan), was useds a model soil. Since this kaolin contains trace of metalsmainly iron), the kaolin was shaken with 0.1 M HCl (kaolin:HClw/w) = 1:4) for 24 h to remove heavy metals. After the proce-

ure, the pH of the model soil was adjusted to 7.0 by additionf aqueous 0.1 M NaOH. The kaolin was filtered and then driedor 24 h in an oven. This treated kaolin was used as a model soiln this study. The chemical property of the kaolin before and

s N.D. (ppm)H 0.26

fter the acid washing was summarized in Table 1. The metalinerals of treated kaolin were analyzed by energy dispersive X-

ay fluorescence spectrometer (EDX) EDX-700HS (Shimadzuo., Japan). The transmission coefficient of the kaolin after acid

reatment was 1.0 × 10−8 cm s−1 and the particle size by the soillassification method was the silt (0.02 mm − 2 �m) of 18% andhe clay (>2 �m) of 82%.

Ferrite solution, which is called as ‘polyferric sulfate’, wasbtained from Lasa Industries Ltd. (Japan) [24]. The compo-ents in this ferrite solution are summarized in Table 2.

.2. Simulator for EK process

In order to investigate the behavior of pollutants in soil byK technology, an apparatus having a small migration chamber

3.0 cm in diameter and 10 cm length) and two electrode cham-ers (3.0 cm in diameter and 5.0 cm length) was prepared withcrylic resins (Fig. 1). To prevent the soil in migration chamberrom leaking into the buffer solution of the electrode chambers,ach chamber was connected using a filter paper of 5B (Advan-ec, Japan) and an O-ring (Kokudo Co., Japan). Two meshed Tilectrodes coated with Pt were inserted into the electrode cham-ers, and the chambers were filled with 0.1 M phosphoric bufferolution [25].

The dc power supply AE-8270 (Atto Co., Japan) or MP-612D (System Instruments Co., Ltd., Japan) was used torovide a constant electric potential across the two electrodes.he current during EK process was measured by this power sup-

Fig. 1. Schematic diagram of electrokinetic remediation apparatus.

664 T. Kimura et al. / Journal of Hazardou

Table 3The condition of all tests in the EK treatment

Test Applied voltage (V) Applied time (h) FTZ Result

1 20 3 EK only Fig. 4a2 20 6 EK only Fig. 4b3 20 12 EK only Fig. 4c4 20 48 EK only Fig. 5c5 20 96 EK only Fig. 4d67

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itctfcdwnopFlTicoprecipitation phenomenon to capture the heavy metal ions inferric hydroxide. It was reported that the ferritization of copperwas progressed through the reactions shown in the followingEqs. (1) and (2) [26–28]. Barrado et al. suggested the coprecipi-

20 24 EK-FTZ Fig. 5a20 48 EK-FTZ Fig. 5b

By adding the copper ion solution prepared with Cu(SO4)nto treated kaolin and mixing them well, the contaminated soilas prepared. The contaminated soil was filled in the half of

n anode side of the migration chamber. The initial concentra-ion of copper was 50.0 ppm and the water content in the alloils was adjusted at 30% using a buffer solution (pH 7.0, 0.1 MaH2PO4/0.1 M NaOH buffer). The copper of 50 mg/kg was

dopted in these experiments. The value is close to a naturalontent in soil and selected for the contamination with a relativeow concentration. The total amount of copper in the migrationhamber was 3.0 mg. The remaining area from the center in theigration chamber to the cathodic chamber, was packed with

he soil containing only buffer solution. The total weight of theoil in the migration chamber was 120 g in every run.

In the case of experiments for EK combined with FTZ, theoil containing ferrite reagent was filled instead of the soil con-aining buffer solution. The concentration of ferrite in the FTZas 1000 ppm (mg/kg) that was an excessive amount for cop-er of 50 mg/kg in the soil. The condition of the all tests wasummarized in Table 3.

.3. Analytical method

After the EK experiment, the soil sample was removed fromhe migration chamber and sliced into several sections. Eachection was provided for the measurement of water content, pHnd the concentration of copper by means shown in the followingections.

.3.1. pH of soilTo measure pH of soil before and after EK treatment, 2.5 ml

istilled water was added to 1.0 g of soil in each sectionw:w = 1:2.5). The measurement method of soil pH in Japan wasecommended by Soil Reaction Commission of Internationalnion of Soil Sciences. And the mixture was shaken at 1500 rpm

t room temperature for 1 h. The pH values of the extracted waterere measured by a digital pH meter M-13 (Horiba Co., Japan).

.3.2. Measurement of copper in soilAfter EK treatment, the amounts of total copper in the soil,

he solution of two electrode chambers and the overflow by EOF

ere determined by the following procedure. Copper ions were

xtracted from 3.0 g of soil in each sliced section by shaking itith 27.0 ml of 1 M HCl (w:w = 1:9) at 1500 rpm for 6 h using

haker M-1000 (EYELA, Japan). After shaking, the mixture

FtN

s Materials 143 (2007) 662–667

f soil and hydrochloric acid was centrifuged at 4000 rpm for5 min using the centrifugal separator 2410 (Kubota Co., Japan).he concentration of total copper ion in the supernatant wasnalyzed by atomic absorption spectrophotometer (AAS), A-000 (Hitachi Co., Japan). The extraction of copper ions fromoil and analysis of copper concentration were carried out byapanese Industrial Standard (JIS) K 0102. The mass balanceor copper in the EK system was within the range of ±10%.

To evaluate the amount of copper insolubilized with ferriten soil, free copper ions in the soil was measured as well ashe total amount of copper. After EK remediation treatment,he free copper ion was extracted from 3.0 g of soil in eachection by adding 27 ml of Milli-Q® water (Millipore Co., USA)w:w = 1:9) and then analyzed by the same method for the totalopper.

. Results and discussion

.1. Ferritization of copper ion in solution

At first, the ferritization of copper ion in the solution wasnvestigated at various pH. Fig. 2 shows the effect of pH andhe amount of ferrite on the normalized concentration of freeopper ion in the solution. After ferritizations, the concentra-ion of free copper ion, which was eluted with Milli-Q® waterrom the ferrite, was determined by AAS. The concentration ofopper ion at every run was almost not changed in acidic con-ition. In alkali solution, however, the concentration of copperas decreased in every runs. Even through Fe2+ and Fe3+ wereot present, the eluted copper ion was decreased at the half levelf the initial concentration, due to the formation of hydroxiderecipitation in the alkali solution. In the presence of Fe2+ ande3+ in the alkali solution, the eluted copper ion was decreased

argely in comparison with that in the absence of ferrite solution.his figure indicates that the pH condition from neutral to alkali

s required for ferritization of copper. The ferritization is one of

ig. 2. Effect of pH generating ferrite of copper. Initial copper concentra-ion = 100 ppm (1.53 mM), Fe3+ = 200 ppm (3.58 mM), buffer solution = 0.1 MaH2PO4/0.1 M HCl or 0.1 M NaOH.

T. Kimura et al. / Journal of Hazardous Materials 143 (2007) 662–667 665

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ig. 3. Effect of diffusion of copper in soil. [Copper] = 50 ppm, applied volt-ge = 0 V, applied time = 72 h.

ation mechanism for Fe2+ and divalent or polyvalent metal ionss Eq. (3) [29]. The precipitation of copper after ferritizationould be separated by the magnetic stirring bar. This indicateshat the ferrite precipitation with copper become magnetic bodynd makes it easy to separate the precipitates from solution.

Cu2+ + (3 − n)Fe2+ + 6OH− → CunFe(3−n)(OH)6 (1)

unFe(3−n)(OH)6 + (1/2)O2 → CunFe(3−n)O4 + 3H2O (2)

xCu2+ + 3FeSO4 + 6NaOH + (1/2)O2

→ CuxFe3−xO4 + 3Na2SO4 + 3H2O + x[Fe2+] (3)

.2. Removal of copper from soil by EK treatment

Since electrolysis of water in each chamber occurred by thepplied constant dc voltage in EK treatment, the solution in thenodic chamber was changed to acid solution and the solution inhe cathodic chamber was to alkali solution. Hydrogen ion gen-rated by the electrolysis of water in the acidic chamber movednto the soil in the migration chamber if pH of the electrodehamber was not controlled. Consequently, the acidic and alkalione in soil appeared during the EK process. The acidic soilondition is suitable for removal of metal in the soil, becauseetal and metal oxide in soil could be changed to metal ions

n acidic condition. Metal ions are also adsorbing strongly byon-exchanging mechanism on the clay mineral of soil. There-ore, in order to shift the ion exchanging equilibration, the acidicondition is essential. On the other hand, alkali condition nearhe cathodic chamber facilitates the ferritization of copper ions.

Fig. 3 shows the distribution of copper and pH of the soil inhe migration chamber after for 72 h without EK treatment. Theorizontal axis of this figure represents the normalized distancerom the anode, that is, 0 of the axis means the edge of the anodichamber and the 1 means the edge of the cathodic chamber. Thenitial copper concentration of the soil in the position of 0–0.5 (a

otted box) in the migration chamber was adjusted to 50 ppm,nd the rest was 0 ppm. Initial pH in the soil was adjusted to 7.0.fter 72 h without EK treatment, the distribution of copper ion

n the soil and the pH of the soil did not change compared with

iiti

ig. 4. Removal of copper in soil on EK. [Copper] = 50 ppm, applied volt-ge = 20 V. Applied time: (a) 3 h, (b) 6 h, (c) 12 h and (d) 96 h.

he initial condition. This shows that copper ions in the soil canot move only by diffusion, and that the analysis methods foropper ions and pH are adequate because the initial condition isepresented by the analysis.

Fig. 4 shows the distribution of the concentration of totalopper and eluted copper and pH of the soil in migration chamberfter applying voltage in EK treatment. After 3 h (Fig. 4a), pHf the soil in nearly each chambers began to be changed byK process. In acidic region, the copper concentration in 0–0.2as decreased, whereas the copper concentration of 0.2–0.3 of

he axis was increased. In neutral pH region in 0.3–0.4 of thexis, the copper concentration was not changed. This indicateshat the copper ion in acidic condition can move in soil easily inhe direction to the cathode [31], but in neutral pH region copperon cannot move, because of ion-exchanging mechanism of clay

ineral.After 6 h, copper was detected even at central position of

he soil in the migration chamber (Fig. 4b). This position is theront of acidic soil and also the front of alkali soil and it isalled as the ‘pH junction’ or ‘pH jump’ [30]. The pH of soilas changed from 2 to 12 abruptly at this position. The total

oncentration of copper in the position of 0.4–0.5 was equal tohe eluted copper concentration. However, the eluted copper inhe position of 0.5–0.6 decreased largely compared with the totalopper concentration at this position. This difference was due tohe formation of hydroxide precipitate of copper in alkali soil.ig. 4c shows the distribution of copper ions after 12 h. Copperoved more to cathodic chamber than that after 6 h.After 96 h (Fig. 4d), all soils in the migration chamber was

ompletely acidified and most of copper ions moved to the vicin-ty of the cathodic chamber. The total copper concentration inhis position was equal to the eluted copper concentration. This

ndicates that copper in the soil is free ionic form and the hydrox-de precipitate of copper ion is also dissolved when all soil inhe migration chamber become acidic soil. Therefore, copperons might move from migration chamber to cathodic cham-

666 T. Kimura et al. / Journal of Hazardous Materials 143 (2007) 662–667

Fig. 5. Insolubilization of copper in soil by EK applied reaction wall of ferrite as a function of time. [Copper] = 50 ppm, [ferrite soil] Fe2+ = 500 ppm, Fe3+ = 1000 ppm,applied voltage = 20 V. Applied time: (a) 24 h, (b) 48 h (EK with PRBs) and (c) 48 h (EK treatment only).

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ig. 6. Current and total amount of EOF during applied voltage by the EK treatmime = 72 h.

er. However, copper ions were slightly detected in the solutionf cathodic chamber and measuring cylinder. The solution inhe cathodic chamber was strong alkali and the surface of soiln contact with the chamber, and the filter paper between the

igration and cathodic chamber was also strong alkali and thenopper ions existed there as hydroxide precipitations.

.3. Insolubilization of copper ions in soil on EK with FTZ

Fig. 5 shows the distribution of the total copper and the elutedopper in the soil of migration chamber with FTZ after applyingoltage by EK. After 24 h, copper ions moved to the cathodichamber (Fig. 5a), but distribution of copper remained in theTZ. The less amount of eluted copper suggested the evidence oferritizing in FTZ. After 48 h, the large difference between totaloncentration and eluted concentration of copper was observedFig. 5b). While the large difference between total and elutedoncentration of copper was not observed in the case of EKreatment without FTZ (Fig. 5c). The results in Fig. 5c showshe FTZ is effective for the immobilization of copper ion. Thats, in FTZ, copper is insolubilized with ferrite reagent and accu-

ulated in the zone. The ratio of the ferritization was 92% byK with FTZ after 48 h.

Fig. 6 shows the current through soil and the overflow carriedy EOF (total amount of EOF) as a function of EK treatmentime. As shown in Fig. 6a, the current of both the treatment of

K with and without FTZ increased for at first 5 h, then theurrent suddenly decreased after 10 h. This decrement of theurrent was thought to be due to the loss of ionic species inoil by neutralization. That is, when the front of acidic and the

ai

a) Current (mA), (b) total amount of EOF (ml). Applied voltage = 20 V, applied

ront of alkali contact each other, neutralization occurs there toanish ionic species such as proton and hydroxide. As shownn Fig. 6b, the total amount of EOF by the EK with FTZ wasecreased compared with the EK treatment without FTZ. Theotal amount of EOF after 72 h by the EK treatment was 76 mlnly and 32 ml by the EK treatment with FTZ. This decrease washought to be due to the difference of the current through soil ashown in Fig. 6a. The current is significant factor for removingopper ions from soil. Therefore, adding much ferrite reagento soil leads to the decrease of the efficiency in the removalf copper from the soil although it is effective for ferritizingopper ions. The precipitation of copper in alkali condition ofK treatment sometimes stopped the flow of current and EOF.he velocities of EOF and electromigration of metal ions

ncreased with increasing potential gradient and current density.owever, Gray reported that the heat generation was caused by

pplying a current density over 5 mA/cm2 [31]. In the presentystem with the voltage gradient of 2.0 V/cm, the heat generationas not observed.The EK technology with FTZ could insolubilize and

ccumulate copper at the limiting position in the soil. Thensolubilization as copper–ferrite of magnetic materials mightacilitate the separation of heavy metals from the soil as well asrom the solution.

. Conclusions

The usefulness of the combined use of the EK remediationnd the FTZ for treatment of the soil contaminated with copperon was demonstrated. In the case of EK treatment with FTZ,

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T. Kimura et al. / Journal of Haza

he large difference between total and eluted concentration ofopper in the zone was observed. This shows that copper ionsere insolubilized by the reaction with ferrite reagent in the

one and was accumulated as copper–ferrite in soil. Therefore,he EK system with FTZ has some advantages, for example:1) it is able to collect heavy metals in a specific zone, then2) to avoid the treatment of a large amount of water producedy EK system and (3) there is a possibility that copper–ferritean be collected and separated by magnet. Although actual fieldcenario is a problem in future, the FTZ is made in the vicinity ofhe cathode around the contaminated site by injecting the ferriteolution into the narrow soil zone, and the electrode position isecided so that the contaminated water from the contaminatedoil is introduced to the FTM by EK process. After EK treatment,he FTZ is dug over and then copper in FTZ is recovered byhe adequate process, such as washing with acid and magneticeparation.

cknowledgement

This work was supported in part by 21st Century Center ofxcellence Program (E-01) funded by Ministry of Education

Culture, Sports, Science and Technology).

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